Pydot features now use pydotplus.
Fixes installation on some machines and test with appveyor.
Restores default center and scale of layout routines.
Fixes various docs including no symbolic links in examples.
Docs can now build using autosummary on readthedocs.org.

New functions for k-clique community finding, flow hierarchy,
union, disjoint union, compose, and intersection operators that work on
lists of graphs, and creating the biadjacency matrix of a bipartite graph.

read/write routines in io.py now handle XGraph() type and
gzip and bzip2 files

optional mapping of type for read/write routine to allow
on-the-fly conversion of node and edge datatype on read

Substantial changes related to digraphs and definitions of
neighbors() and edges(). For digraphs edges=out_edges.
Neighbors now returns a list of neighboring nodes with
possible duplicates for graphs with parallel edges
See https://networkx.lanl.gov/trac/ticket/24

Addition of out_edges, in_edges and corresponding out_neighbors
and in_neighbors for digraphs. For digraphs edges=out_edges.